1. Field of the Invention
2. Description of the Prior Art
The present invention relates generally to an electronic component mounting apparatus and, more particularly, to the apparatus for automatically mounting on printed circuit boards electronic components such as, for example, transistors, capacitors and/or resistors.
Hitherto, the electronic component mounting apparatus is well known which comprises a carrier turntable having a plurality of suction heads mounted thereon in radial orientation for holding electronic components by the action of a substantial vacuum developed inside the suction heads so that, during the rotation of the carrier turntable, the electronic components sucked by the respective suction heads can be successively mounted at high speed on a printed circuit board. An example of this prior art component mounting apparatus is illustrated in FIG. 8 in partial top plan view.
Referring to FIG. 8, the carrier turntable is generally identified by 100 and has its undersurface carrying a circular row of mounting heads 101 for movement up and down, which row is coaxial with the axis of rotation of the carrier turntable 100. A component delivery unit 102 such as, for example, a tray or a carrier tape, and a movable bench 103 such as, for example, an X-Y table, are disposed beneath the carrier turntable 100.
The illustrated prior art mounting apparatus is so designed that, after any one of the mounting heads 101 having been lowered has picked up the electronic component C from the delivery unit 102, the carrier turntable 100 can be intermittently rotated in a direction shown by N to bring the electronic component C to a position immediately above the movable bench 103 and is then lowered to mount the electronic component C onto a printed circuit board 104 supported on the movable bench 103.
A drive mechanism used in the illustrated prior art mounting apparatus for driving the mounting heads 101 is shown in FIG. 9. As shown in FIG. 9, the drive mechanism comprises a drive box 105 and a drive motor 106 for driving the carrier turntable 100 in the direction N intermittently, an endless toothed belt 107, a first motion translator 108 comprised of a cam member 108a and a cam follower 108b, a first motion transmitting lever 109 having one end carrying the cam follower 108b, a tie rod 110 connected at one end with the other end of the motion transmitting lever 109, a second motion transmitting lever 111 operatively connected at one end with the other end of the tie rod 110, a second motion translator 112 comprised of a slider 112a drivingly coupled with the other end of the second motion transmitting lever 111, a head carrier shaft 113 for each mounting head 101, and a nozzle 114 protruding downwardly from the respective mounting head 101 carried by the associated carrier shaft 113.
The prior art component mounting apparatus of the construction shown in and described with reference to FIGS. 8 and 9 operates in the following manner.
Assuming that the drive motor 106 is driven to rotate the cam member 108a through the motion transmitting belt 107, the cam follower 108b moves up and down in contact with the peripheral cam face of the cam member 108a, causing the first motion transmitting lever 109 to be reciprocated about a pivot pin 109a in opposite directions shown by the arrow a. The pivotal motion of the first motion transmitting lever 109 is transmitted to the second motion transmitting lever 111 through the tie rod 110 then reciprocatingly moving horizontally in opposite directions shown by the arrow b, causing the slider 112a to move up and down with the second motion transmitting lever 111 reciprocatingly pivoted about a pivot pin 111a in opposite directions shown by the arrow c. Consequent upon the up and down movement of the slider 112a, the head carrier shaft 113 is reciprocated in a vertical direction perpendicular to the plane of rotation of the carrier turntable 100. In particular, when the shaft 113 is lowered with the associated mounting head 101 approaching the printed circuit board 104, the electronic component C carried by such mounting head can be mounted onto the printed circuit board 104.
The up and down movement of the carrier shaft 113 takes place even when the electronic component C is to be picked up from the delivery unit 102.
The stroke of movement of any one of the mounting heads 101 employed in the prior art component mounting apparatus is fixed as determined by the configuration of the cam member 108a and the cam member 108a is therefore so designed as to realize a desired stroke of movement of any one of the mounting heads 101. This stroke is generally chosen in consideration of the average thickness of the electronic components handled by the mounting apparatus.
Accordingly, where the stroke of movement of any one of the mounting heads is desired to be changed, the prior art component mounting apparatus requires the cam member to be replaced by another cam member of different configuration required to achieve the desired stroke. Accordingly, not only is the manufacture of the plural cam members of different configuration time-consuming, but the prior art component mounting apparatus has a problem in that the replacement of one particular cam member with another one is not easy to accomplish and the machine has to be held inoperative during the replacement.
In addition, since the prior art component mounting apparatus of the type referred to above is such that the stroke of movement of the mounting heads is fixed, the apparatus cannot accommodate the electronic components of different thickness. Therefore, where the electronic component desired to be mounted on the printed circuit board has a thickness greater than the average thickness for which the stroke of movement of the mounting heads has been determined, the stroke Sm will be too excessive for such electronic component as shown in FIG. 10(a) and, accordingly, when any one of the mounting head 101 is lowered, the associated nozzle 114 will press deep the electronic component C during the mounting of the latter onto the printed circuit board 104 on the movable bench 102, causing such electronic component C to be eventually impaired or damaged. A similar problem may occur when the mounting head is lowered at the delivery station in readiness for the picking up the electronic component carried by the delivery unit 103.
Conversely, where the electronic component desired to be mounted on the printed circuit board has a thickness smaller than the average thickness for which the stroke of movement of the mounting heads has been determined, the stroke Sm will be too short for such electronic component as shown in FIG. 10(b) and, accordingly, when any one of the mounting head 101 is lowered, the associated nozzle 114 will be spaced a substantial distance t, shown in FIG. 10(b), from the electronic component part C desired to be mounted thereby failing to pick it up at the delivery station from the delivery unit. Also, even when the respective mounting head 101 is lowered at the mounting station above the movable bench 103, a gap corresponding to the distance t will be formed between the component part C, sucked by the mounting head 114, and the printed circuit board 104 as shown in FIG. 10(c) and the electronic component C may be released from the mounting head 114 while afloat above the printed circuit board 104. Once this occur, the electronic component C may be dropped by the effect of a gravitational force onto the printed circuit board 104, failing to assume a proper position relative to the printed circuit board 104.
As can readily be understood from the above discussion on the prior art component mounting apparatus, it is a very important underlying problem to provide that the stroke of movement of the mounting heads can be adjusted easily and properly so that the component mounting apparatus can accommodate electronic components of different sizes.
There is well known a means for adjusting the stroke of movement of the mounting heads, which means comprises a means for supporting the movable bench for movement close to and away from the mounting heads. This prior art adjusting means, however, has a problem in that it cannot precisely accommodate a change in thickness of the electronic components desired to be mounted and is, therefore, so designed as to permit the movable bench to assume one of elevated and lowered positions. Accordingly, when an electronic component having a thickness generally intermediate of the stroke of movement of the movable bench is to be mounted, misalignment and/or misplacement of such electronic component tend to occur often.
In addition, considering that the delivery unit is generally installed on a table fixed above the floor, the use of the upwardly and downwardly shiftable bench in combination with the fixed delivery unit is not possible and, therefore, the adjusting means referred to above cannot work satisfactorily at the delivery station.
It may, however, be contemplated that an adjusting means similar to the adjusting means for supporting the movable bench for movement up and down may be employed in the delivery unit for supporting the latter for movement up and down in unison with the movement of the bench. In such case, since the two adjusting means are required one for each of the bench and the delivery unit, the apparatus as a whole will become bulky and expensive to make besides the use of complicated elevating means as well as control means.